Physicists Optically Manipulate Abrikosov Vortices

Scientists from the University of Bordeax and the Moscow Institute of Physics and Technology (MIPT) have performed a unique experiment involving the optical manipulation of individual Abrikosov vortices in a superconductor. Their results could help design new logic units based on quantum principles for use in supercomputers.

Superconductivity — zero electrical resistance — occurs in certain materials in the temperature range from −273 to −70 degrees Celsius. When a material transitions into this state, the magnetic flux fields are expelled. A superconductor either has all magnetic field lines ejected from its interior or allows partial penetration of the magnetic field.

The randomly distributed vortices in the superconducting sample (left) have been repositioned into a pattern forming the letters "AV," which stands for Abrikosov vortices (right). Courtesy of MIPT.
The phenomenon of partial penetration was explained in 1957 by Alexei Abrikosov, for which he was awarded the 2003 Nobel Prize in Physics. Abrikosov demonstrated that type-II superconductors — materials that do not exhibit complete magnetic field expulsion — can only be penetrated by discrete magnetic flux units. As the field within a superconductor grows stronger, this gives rise to the cylindrical current loops known as Abrikosov vortices.

"Type-II superconductors are used everywhere: from medicine to energetics and other industries. Their properties are determined by the 'vortex matter,' which makes research into vortices and finding ways to manipulate them very important for modern physics," said Ivan Veshchunov, a researcher at the Laboratory of Topological Quantum Phenomena in Superconducting Systems at MIPT.

To manipulate the vortices, the scientists used a focused laser beam, as the vortices are attracted to higher temperatures in a superconductor.

Because the vortices act as magnetic flux quanta, they can be used to shape the overall magnetic flux profile, enabling physicists to perform various experiments with superconductors. While a triangular vortex lattice occurs naturally in certain magnetic fields, other types of lattices and devices like vortex lenses can be created by moving vortices around.

Professor Brahim Lounis from the University of Bordeax told Photonics Media that this technology is the most promising in terms of the design of superfast memory for quantum computers.

“The interplay between photons and single flux quanta should open up novel research directions in quantum computation based on braiding and entanglement of vortices; Josephson switches of electric current; or optically controlled elements of rapid single flux quantum logics (RSFQ),” said Lounis.

RSFQ-based logic elements are already used in digital-to-analog and analog-to-digital converters, high-precision magnetometers and memory cells. A number of prototype computers based on this technology have been developed including the FLUX-1 designed by a team of U.S. engineers. However, the RSFQ logic elements in these computers are mostly controlled by electrical impulses. Optically controlled logic is one of the emerging trends in superconducting systems.

Professor Lounis said optical manipulation of individual vortices is challenging and prior to their experiment, was only achieved with scanning local probe techniques. These techniques are intrinsically slow and difficult to implement.

“With our simple far-field optical method, single vortices can be manipulated over large distances; they are only limited by the field of view of the microscope objective (~1 mm) and at high driving speeds only limited by the ratio of the hotspot size (~1 μm) to the thermal response time,” said Lounis. “Our method opens the way to fast optical operations.”

The experiments performed by the scientists serve as a proof of concept for an approach that could be used in future research into Abrikosov vortices.